<!DOCTYPE html>
<html lang="en">

  <head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>网页底部小鱼游动特效</title>
    <style>
      .container {
        width: 100%;
        height: 200px;
        position: fixed;
        z-index: -1;
        opacity: 0.37;
        bottom: 0;
        left: 0;
        background-color: rgb(1, 195, 243);
      }
    </style>
  </head>

  <body>
    <div id="jsi-flying-fish-container" class="container"></div>
    <script>
      window.onload = () => {
        RENDERER.init();
      }
      var RENDERER = {
        POINT_INTERVAL: 5,
        FISH_COUNT: 3,
        MAX_INTERVAL_COUNT: 50,
        INIT_HEIGHT_RATE: 0.5,
        THRESHOLD: 50,

        init: function () {
          this.setParameters();
          this.reconstructMethods();
          this.setup();
          this.bindEvent();
          this.render();
        },
        setParameters: function () {
          this.$window = window;
          this.$document = document.body
          this.$container = document.getElementById('jsi-flying-fish-container');
          this.$canvas = document.createElement('canvas');
          this.$container.appendChild(this.$canvas)
          this.context = this.$canvas.getContext('2d');
          this.points = [];
          this.fishes = [];
          this.watchIds = [];
        },
        createSurfacePoints: function () {
          var count = Math.round(this.width / this.POINT_INTERVAL);
          this.pointInterval = this.width / (count - 1);
          this.points.push(new SURFACE_POINT(this, 0));

          for (var i = 1; i < count; i++) {
            var point = new SURFACE_POINT(this, i * this.pointInterval),
              previous = this.points[i - 1];

            point.setPreviousPoint(previous);
            previous.setNextPoint(point);
            this.points.push(point);
          }
        },
        reconstructMethods: function () {
          this.watchWindowSize = this.watchWindowSize.bind(this);
          this.jdugeToStopResize = this.jdugeToStopResize.bind(this);
          this.startEpicenter = this.startEpicenter.bind(this);
          this.moveEpicenter = this.moveEpicenter.bind(this);
          this.reverseVertical = this.reverseVertical.bind(this);
          this.render = this.render.bind(this);
        },
        setup: function () {
          this.points.length = 0;
          this.fishes.length = 0;
          this.watchIds.length = 0;
          this.intervalCount = this.MAX_INTERVAL_COUNT;
          this.width = this.$container.offsetWidth;
          this.height = this.$container.offsetHeight;
          this.fishCount = this.FISH_COUNT * this.width / 500 * this.height / 500;
          this.$canvas.width = this.width;
          this.$canvas.height = this.height;
          this.reverse = false;

          this.fishes.push(new FISH(this));
          this.createSurfacePoints();
        },
        watchWindowSize: function () {
          this.clearTimer();
          this.tmpWidth = this.$window.width;
          this.tmpHeight = this.$window.height;
          this.watchIds.push(setTimeout(this.jdugeToStopResize, this.WATCH_INTERVAL));
        },
        clearTimer: function () {
          while (this.watchIds.length > 0) {
            clearTimeout(this.watchIds.pop());
          }
        },
        jdugeToStopResize: function () {
          var width = this.$window.width(),
            height = this.$window.height(),
            stopped = (width == this.tmpWidth && height == this.tmpHeight);

          this.tmpWidth = width;
          this.tmpHeight = height;

          if (stopped) {
            this.setup();
          }
        },
        bindEvent: function () {

          this.$window.onresize = this.watchWindowSize;
          this.$container.onclick = this.reverseVertical;
          this.$container.onmouseenter = this.startEpicenter;
          this.$container.addEventListener('onmousemove', this.moveEpicenter);

        },
        getAxis: function (event) {

          var offset = this.getOffset(this.$container);
          return {
            x: event.clientX - offset.left + this.$document.scrollLeft,
            y: event.clientY - offset.top + this.$document.scrollTop
          };
        },

        getOffset: function (Node, offset) {
          if (!offset) {
            offset = {};
            offset.top = 0;
            offset.left = 0;
          }
          if (Node == document.body) {
            //当该节点为body节点时，结束递归        
            return offset;
          }
          offset.top += Node.offsetTop; offset.left += Node.offsetLeft;
          return this.getOffset(Node.parentNode, offset);//向上累加offset里的值
        },
        startEpicenter: function (event) {
          this.axis = this.getAxis(event);
        },
        moveEpicenter: function (event) {
          var axis = this.getAxis(event);

          if (!this.axis) {
            this.axis = axis;
          }
          this.generateEpicenter(axis.x, axis.y, axis.y - this.axis.y);
          this.axis = axis;
        },
        generateEpicenter: function (x, y, velocity) {
          if (y < this.height / 2 - this.THRESHOLD || y > this.height / 2 + this.THRESHOLD) {
            return;
          }
          var index = Math.round(x / this.pointInterval);

          if (index < 0 || index >= this.points.length) {
            return;
          }
          this.points[index].interfere(y, velocity);
        },
        reverseVertical: function () {
          this.reverse = !this.reverse;

          for (var i = 0, count = this.fishes.length; i < count; i++) {
            this.fishes[i].reverseVertical();
          }
        },
        controlStatus: function () {
          for (var i = 0, count = this.points.length; i < count; i++) {
            this.points[i].updateSelf();
          }
          for (var i = 0, count = this.points.length; i < count; i++) {
            this.points[i].updateNeighbors();
          }
          if (this.fishes.length < this.fishCount) {
            if (--this.intervalCount == 0) {
              this.intervalCount = this.MAX_INTERVAL_COUNT;
              this.fishes.push(new FISH(this));
            }
          }
        },
        render: function () {
          requestAnimationFrame(this.render);
          this.controlStatus();
          this.context.clearRect(0, 0, this.width, this.height);
          this.context.fillStyle = 'hsl(0, 0%, 95%)';

          for (var i = 0, count = this.fishes.length; i < count; i++) {
            this.fishes[i].render(this.context);
          }
          this.context.save();
          this.context.globalCompositeOperation = 'xor';
          this.context.beginPath();
          this.context.moveTo(0, this.reverse ? 0 : this.height);

          for (var i = 0, count = this.points.length; i < count; i++) {
            this.points[i].render(this.context);
          }
          this.context.lineTo(this.width, this.reverse ? 0 : this.height);
          this.context.closePath();
          this.context.fill();
          this.context.restore();
        }
      };
      var SURFACE_POINT = function (renderer, x) {
        this.renderer = renderer;
        this.x = x;
        this.init();
      };
      SURFACE_POINT.prototype = {
        SPRING_CONSTANT: 0.03,
        SPRING_FRICTION: 0.9,
        WAVE_SPREAD: 0.3,
        ACCELARATION_RATE: 0.01,

        init: function () {
          this.initHeight = this.renderer.height * this.renderer.INIT_HEIGHT_RATE;
          this.height = this.initHeight;
          this.fy = 0;
          this.force = { previous: 0, next: 0 };
        },
        setPreviousPoint: function (previous) {
          this.previous = previous;
        },
        setNextPoint: function (next) {
          this.next = next;
        },
        interfere: function (y, velocity) {
          this.fy = this.renderer.height * this.ACCELARATION_RATE * ((this.renderer.height - this.height - y) >= 0 ? -1 : 1) * Math.abs(velocity);
        },
        updateSelf: function () {
          this.fy += this.SPRING_CONSTANT * (this.initHeight - this.height);
          this.fy *= this.SPRING_FRICTION;
          this.height += this.fy;
        },
        updateNeighbors: function () {
          if (this.previous) {
            this.force.previous = this.WAVE_SPREAD * (this.height - this.previous.height);
          }
          if (this.next) {
            this.force.next = this.WAVE_SPREAD * (this.height - this.next.height);
          }
        },
        render: function (context) {
          if (this.previous) {
            this.previous.height += this.force.previous;
            this.previous.fy += this.force.previous;
          }
          if (this.next) {
            this.next.height += this.force.next;
            this.next.fy += this.force.next;
          }
          context.lineTo(this.x, this.renderer.height - this.height);
        }
      };
      var FISH = function (renderer) {
        this.renderer = renderer;
        this.init();
      };
      FISH.prototype = {
        GRAVITY: 0.4,

        init: function () {
          this.direction = Math.random() < 0.5;
          this.x = this.direction ? (this.renderer.width + this.renderer.THRESHOLD) : -this.renderer.THRESHOLD;
          this.previousY = this.y;
          this.vx = this.getRandomValue(4, 10) * (this.direction ? -1 : 1);

          if (this.renderer.reverse) {
            this.y = this.getRandomValue(this.renderer.height * 1 / 10, this.renderer.height * 4 / 10);
            this.vy = this.getRandomValue(2, 5);
            this.ay = this.getRandomValue(0.05, 0.2);
          } else {
            this.y = this.getRandomValue(this.renderer.height * 6 / 10, this.renderer.height * 9 / 10);
            this.vy = this.getRandomValue(-5, -2);
            this.ay = this.getRandomValue(-0.2, -0.05);
          }
          this.isOut = false;
          this.theta = 0;
          this.phi = 0;
        },
        getRandomValue: function (min, max) {
          return min + (max - min) * Math.random();
        },
        reverseVertical: function () {
          this.isOut = !this.isOut;
          this.ay *= -1;
        },
        controlStatus: function (context) {
          this.previousY = this.y;
          this.x += this.vx;
          this.y += this.vy;
          this.vy += this.ay;

          if (this.renderer.reverse) {
            if (this.y > this.renderer.height * this.renderer.INIT_HEIGHT_RATE) {
              this.vy -= this.GRAVITY;
              this.isOut = true;
            } else {
              if (this.isOut) {
                this.ay = this.getRandomValue(0.05, 0.2);
              }
              this.isOut = false;
            }
          } else {
            if (this.y < this.renderer.height * this.renderer.INIT_HEIGHT_RATE) {
              this.vy += this.GRAVITY;
              this.isOut = true;
            } else {
              if (this.isOut) {
                this.ay = this.getRandomValue(-0.2, -0.05);
              }
              this.isOut = false;
            }
          }
          if (!this.isOut) {
            this.theta += Math.PI / 20;
            this.theta %= Math.PI * 2;
            this.phi += Math.PI / 30;
            this.phi %= Math.PI * 2;
          }
          this.renderer.generateEpicenter(this.x + (this.direction ? -1 : 1) * this.renderer.THRESHOLD, this.y, this.y - this.previousY);

          if (this.vx > 0 && this.x > this.renderer.width + this.renderer.THRESHOLD || this.vx < 0 && this.x < -this.renderer.THRESHOLD) {
            this.init();
          }
        },
        render: function (context) {
          context.save();
          context.translate(this.x, this.y);
          context.rotate(Math.PI + Math.atan2(this.vy, this.vx));
          context.scale(1, this.direction ? 1 : -1);
          context.beginPath();
          context.moveTo(-30, 0);
          context.bezierCurveTo(-20, 15, 15, 10, 40, 0);
          context.bezierCurveTo(15, -10, -20, -15, -30, 0);
          context.fill();

          context.save();
          context.translate(40, 0);
          context.scale(0.9 + 0.2 * Math.sin(this.theta), 1);
          context.beginPath();
          context.moveTo(0, 0);
          context.quadraticCurveTo(5, 10, 20, 8);
          context.quadraticCurveTo(12, 5, 10, 0);
          context.quadraticCurveTo(12, -5, 20, -8);
          context.quadraticCurveTo(5, -10, 0, 0);
          context.fill();
          context.restore();

          context.save();
          context.translate(-3, 0);
          context.rotate((Math.PI / 3 + Math.PI / 10 * Math.sin(this.phi)) * (this.renderer.reverse ? -1 : 1));

          context.beginPath();

          if (this.renderer.reverse) {
            context.moveTo(5, 0);
            context.bezierCurveTo(10, 10, 10, 30, 0, 40);
            context.bezierCurveTo(-12, 25, -8, 10, 0, 0);
          } else {
            context.moveTo(-5, 0);
            context.bezierCurveTo(-10, -10, -10, -30, 0, -40);
            context.bezierCurveTo(12, -25, 8, -10, 0, 0);
          }
          context.closePath();
          context.fill();
          context.restore();
          context.restore();
          this.controlStatus(context);
        }
      };
    </script>
  </body>

</html>